Radiation sensitive compositions comprising complexing polar compound and methods of use thereof

ABSTRACT

The present invention provides radiation sensitive compositions and methods that comprise novel means for providing relief images of enhanced resolution. In one aspect the invention provides a method for controlling diffusion of photogenerated acid comprising adding a polar compound to a radiation sensitive composition and applying a layer of the composition to a substrate; exposing the composition layer to activating radiation whereby a latent image is generated comprising a distribution of acid moieties complexed with the polar compound; and treating the exposed composition layer to provide an activating amount of acid.

BACKGROUND OF THE INVENTION

[0001] 1. Introduction

[0002] The invention relates to radiation sensitive compositions such asphotoresists that provide relief images of enhanced resolution. Moreparticularly, the invention relates to compositions and methods thatcomprise novel means for treating photoacid-generating compositions toprovide relief images of enhanced resolution and to control diffusion ofphotogenerated acid.

[0003] 2. Background Art

[0004] Photoresists are used to form photosensitive films used fortransfer of an image to a substrate. After a coating of a photoresist isformed on a substrate, the coating is selectively exposed through aphotomask to a source of activating radiation. The photomask has areasthat are opaque to activating radiation and other areas that aretransparent to activating radiation. Exposure to activating radiationprovides a photoinduced chemical transformation of the photoresistcoating to thereby transfer the pattern of the photomask to the resistcoated substrate. Following exposure, the photoresist is developed toprovide a relief image that permits selective processing of thesubstrate.

[0005] A photoresist can be either positive-acting or negative-acting.For most negative photoresists, those coating layer portions that areexposed to activating radiation polymerize or crosslink in a reactionbetween a photoactive compound and polymerizable reagents of the resistcomposition. Consequently, the exposed coating portions are renderedless soluble in a developer solution than unexposed portions. For apositive-acting photoresist, exposed portions are rendered more solublein a developer solution while areas not exposed remain comparativelyless developer soluble.

[0006] Following development of a photoresist coating, portions of thesubstrate bared by development may be altered such as by chemicaletching or plating. The historical background, types and processing ofconventional photoresists are described by DeForest, PhotoresistMaterials and Processes, McGraw Hill Book Company, New York, ch. 2,1975, and by Moreau, Semiconductor Lithography, Principles, Practicesand Materials, Plenum Press, New York, ch. 2 and 4, 1988, bothincorporated herein for their teaching of photoresist compositions andmethods of making and using the same.

[0007] Most commercial photoresist formulations, both positive andnegative, comprise a film forming resin binder and a radiation sensitivecomponent. Many of the film forming binders in use are phenolic resins.For example, most positive acting photoresists currently in commercialuse comprise a novolak resin and a naphthoquinone diazide sulfonic acidester photoactive compound where the novolak resin is the reactionproduct of formaldehyde and a phenol. Examples of such photoresists aredisclosed in U.S. Pat. Nos. 4,377,631 and 4,404,272, both incorporatedherein by reference. Another class of positive acting photoresistscomprise a poly(vinylphenol) and a naphthoquinone diazide acid ester.Examples of these photoresists are disclosed in U.S. Pat. Nos. 3,869,292and 4,439,516, both incorporated herein by reference.

[0008] Many negative acting photoresists also utilize phenolic resins asthe film-forming component of the resist. For example, photoresistcompositions of particular utility in high resolution deep-UVlithography have been developed based on the use of a photoacidgenerator sensitive to selective wavelengths of radiation, acrosslinking agent, and a phenolic, acid-hardening, polymeric binder. Inthese systems, radiation is used to cleave the photoacid generator, thuscreating a strongly acidic environment. Upon subsequent heating (aprocessing step referred to as the “post exposure bake”), the generatedacid activates the crosslinking agent to react with the phenolic binderand thereby form a base insoluble negative image (negative-tone resist).The acid acts as a catalyst for the crosslinking, i.e., there are manycrosslinking events per unit of acid generated in the film. Resists thatrely on acid catalysts, such as these acid-hardening resists, have beenclassified generally as “chemically amplified photoresists”.

[0009] In addition to catalyzed crosslinking, other chemically amplifiedmechanisms are known, for example, catalyzed deprotection. Exemplary ofsuch a system is a positive-tone resist comprising a phenolic resin, aradiation sensitive component which generates acid upon irradiation, anda dissolution inhibitor which is not photosensitive itself, but ischemically decomposed in an acid-catalyzed deprotection reaction. Aswith the above described negative-acting system, the acid catalyst iscatalytic, inducing a series of deprotection reactions upon heatingduring the post exposure bake.

[0010] More specifically, a deprotection process can be represented bythe following equations:

AG+hv→AH+G→A⁻+H⁺+G  Acid Generation Reaction

H⁺Poly-O-p→Poly-OH+H⁺  Deprotection Reaction

[0011] In the above reactions, the acid-generator (AG) molecule isconverted to a strong acid (AH) upon absorption of a photon (hv), i.e.,upon exposure to activating radiation. The acid proton affects thedesired deprotection reaction of the protected polymer (Poly-O-p, wherePoly-O is a hydroxyl-substituted polymer and p is a protecting group) toprovide the deprotected polymer (Poly-OH) at a rate which is a functionof the acid concentration [H⁺], temperature, diffusion rate of the acidin the polymer matrix and the process environment. A crosslinkingmechanism operates similarly, the acid proton affecting the reactionbetween the crosslinker and the reactive polymer of the composition.

[0012] Adequate resolution of a patterned image generally requires thatthe radiation generated acid concentration, [H⁺], remain substantiallyconstant within the exposed regions of a layer of the composition. Theexposure process defines the latent image by transferring information tothe resist coating layer by means of the phototool and the exposureradiation. This information is stored in the resist as photogeneratedacid. Any loss of this information (i.e., acid) into unexposed regionsof the resist, or into the substrate or environment can reduce theresolution of the transferred image.

[0013] In chemically amplified resists, it is generally important tohave sufficient diffusion of photogenerated acid so that enoughcatalytic conversions occur to provide required photospeed. On the otherhand and as discussed above, it is also important to limit diffusion ofphotogenerated acid to avoid information loss from exposed regions of acoating layer. Striking a satisfactory balance between these twoobjectives, however, can be difficult. Photogenerated acid often tendsto diffuse into unexposed regions of a photoresist coating layer, orinto the environment or the substrate. Upon subsequent heating duringthe post exposure bake, the acid-catalyzed reaction will occur in thoseunexposed regions where the acid has diffused, compromising resolutionof the patterned image.

[0014] Methods for controlling diffusion of acid through an exposedphotoresist layer have included redesign of the polymer matrix toprovide large molecules to slow movement of the photogenerated proton,or to incorporate large molecules of photoacid compounds which generatelarge acid molecules. The use of large molecules has the disadvantage ofdecreasing the number of catalytic cycles for the chemically amplifiedprocess, thus decreasing the sensitivity of the resist.

[0015] Another method to control acid diffusion has been to limit theperiod between exposure and the post exposure bake. This can requiredesign of relatively sophisticated and more costly interchanges betweenthe phototool and baking apparatus.

SUMMARY OF THE INVENTION

[0016] The present invention provides radiation sensitive compositionsand methods for treating such compositions, including methods forenhancing resolution of the relief image of a radiation sensitivecomposition and methods for controlling diffusion of photogeneratedacid. The compositions of the invention may include various types ofresin matrix systems and acid generators and comprise a means ofeffectively controlling loss of contrast due to the effects of aciddiffusion during post exposure residence times. The compositionspreferably comprise phenol-based resin systems. As used herein, the term“acid generator” refers to a compound capable of generating acid uponexposure to activating radiation.

[0017] The invention is based on the discovery that addition of certainpolar compounds to a photoacid-generating composition provides enhancedresolution of images patterned in said compositions. It is believed theaddition of such polar compounds results in the formation of a complexof the polar compound and photogenerated acid. By selecting anappropriate polar compound, an activating amount of acid is liberatedfrom the complex during the post exposure bake to effect the desiredacid-catalyzed reaction (e.g., deprotection or crosslinking). Bycomplexing the photogenerated acid with the polar compound, diffusion ofthat acid out of exposed regions is prevented or at least significantlyinhibited. Consequently the invention enhances resolution of a patternedimage relative to prior systems, particularly when processing conditionsimpose delay between imaging and the post exposure bake.

[0018] Thus in one aspect the invention provides a method for treating aphotoacid-generating composition comprising adding a suitable polarcompound to the composition. In another aspect the invention providesthe method of adding a polar compound to a radiation sensitivecomposition such as a photoresist and applying a layer of thecomposition to a substrate; exposing the composition layer to activatingradiation whereby a latent image comprising acid moieties complexed withthe polar compound is generated; and treating the exposed compositionlayer to provide an activating amount of acid from the complex. Theexposed composition is preferably treated by heating the layer to atemperature sufficient to provide an activating amount of acid.

[0019] The polar compound has one or more moieties that can serve as abase and complex with the photogenerated acid at room temperature.Amines are preferred moieties. The polar compound should be compatiblewith the resist and resist processing conditions. For example, aneffective amount of the polar compound preferably should remain in theradiation sensitive composition after any pre-exposure soft bake.Further, the polar compound should have an appropriate pK_(a) so that anactivating amount of acid is released from the formed complex during thepost exposure bake. If the polar compound has a pK_(a) value that is toohigh, sufficient acid may not be liberated from the acid-polar compoundcomplex at post exposure bake temperatures and thereby inhibit orprevent the desired acid-catalyzed reaction. As discussed infra,effective amounts of the polar compound can vary with the basicity ofthe polar compound.

[0020] Novel articles of manufacture also are provided consisting ofsubstrates coated the compositions of the invention.

[0021] The term “activating amount of acid” as used herein means anamount of acid sufficient to catalyze a desired reaction (e.g.,deprotection or crosslinking) substantially throughout an exposed regionof a coating layer of a photoacid-generating composition, and to therebyprovide a solubility differential sufficient between exposed andunexposed regions of the coating layer to yield a relief image upondevelopment.

[0022] The terms “crosslink” and “crosslinking” as used herein refer toany reaction of the crosslinking agent(s) of the compositions of theinvention that results in reduced developer solubility. For example, theterms refer to, but are not limited to, any reaction that reduces thenumber of free phenolic hydroxyl sites of a phenol-based polymer, suchas the reaction of a crosslinker agent with multiple hydroxyl sites aswell as reaction of a crosslinker agent with a single hydroxyl site.

DETAILED DESCRIPTION OF THE INVENTION

[0023] The polar compounds useful in the invention are characterized byhaving one or more moieties that can complex with photogenerated acid. Acomplex of the polar compound and acid should release an activatingamount of acid upon heating at temperatures of the post exposure bake toeffect the desired acid-catalyzed reaction. Typically post exposure baketemperatures range from about 50° C. or greater. Hence a complex ofphotogenerated acid and the polar compound suitably releases anactivating amount of acid at about 50° C. or greater. Post exposurebakes of 80° C., 100° C., 110° C., 120° C., 140° C. or greater arecommon; therefore release of an activating amount of acid at any ofthese temperatures or greater can be suitable.

[0024] It is common to perform a pre-exposure bake after coating aliquid photosensitive composition on a surface to remove solvents. Sucha pre-exposure bake is typically conducted at temperatures of 90° C. orless. It is thus preferred that a sufficient amount of the polarcompound remain disposed within a radiation sensitive composition, andnot be volatilized, at such pre-exposure bake temperatures, so that aneffective amount of the polar compound is present to complex with acidgenerated during imaging.

[0025] The polar compounds of the invention comprise one or more polarfunctional groups so that the compound is sufficiently basic to complexwith photogenerated acid. Suitable polar functional groups include, forexample, ether, ester, amide (including N-substituted amides andN-unsubstituted amides such as acetamide and urea) and amines. Amineshave been found to be preferred polar moieties.

[0026] For the photogenerated acid-polar compound complex to release anactivating amount of acid during post exposure bake temperatures, thepK_(a) of the polar compound must be sufficiently low. As used herein,the term “pK_(a)” is used in accordance with its art recognized meaning,that is, pK_(a) is the negative log (to the base 10) of the dissociationconstant of the polar compound in aqueous solution at about roomtemperature.

[0027] Effective results can be achieved if the pK_(a) of the polarcompound is about 8.0 or less, although polar compounds having a pK_(a)of greater than about 8.0 can be suitable (e.g., a pK_(a) of about 9.0or less) provided a sufficiently high temperature post-exposure bake isemployed to release an activating amount of acid from the polarcompound-photogenerated acid complex. Preferably, a polar compound isused that provides a pK_(a) of about 7.0 or less, more preferably apK_(a) of about 4.0 or less, still more preferably a pK_(a) of about 3.2or less. It should be appreciated, however, that the environments inwhich the polar compounds of the invention are typically used, namelyorganic-based photoacid-generating compositions, are different than theaqueous solutions in which the above pK_(a) values are determined.Hence, polar compounds having pK_(a) values somewhat outside the abovedescribed preferred ranges also may be suitable for purposes of theinvention.

[0028] It also should be appreciated that the weaker the basicity of thepolar compound, relatively larger amounts of the polar compound may needto be added to a photoacid-generating composition to form a complex ofthe photogenerated acid and the polar compound. Conversely, the strongerthe basicity of the polar compound, a relatively lower concentration ofthe polar compound will be required to form a complex of thephotogenerated acid and the polar complex, and relatively lesser amountsof the polar compound can be added to a photoacid-generating compositionto realize effective results, for example enhanced resolution of apatterned image of the composition.

[0029] As indicated above, amines are preferred polar compounds.Suitable amines will include, for example, aryl substituted aminesincluding phenyl substituted amines such as 4-(p-aminobenzoyl) aniline,4-benzyl aniline, 2-bromo aniline, o-chloro aniline, m-chloro aniline,3,5-dibromo aniline, 2,4-dichloro aniline, N,N-dimethyl-3-nitro aniline,2-fluoro aniline, 2-iodo aniline, 3-nitro aniline, 4-nitro aniline,2-amino benzoic acid, 4-aminoazo benzene, 4-dimethylaminoazo benzene,n-diphenylamine, and phenyl glycine; cyclic amines (includingnitrogen-containing aromatics) such as nicotine, 3-acetyl piperidine,proline, hydroxy proline, 2-amino-4-hydroxy pteridine, purine, 8-hydroxypurine, pyrazine, 2-methyl pyrazine, methylamino pyrazine, pyridazine,2-amino pyrimidine, 2-amino-5-nitro pyrimidine, 3-bromo pyridine,3-chloro pyridine, 2-hydroxy pyridine, 4-hydroxy pyridine, quinazoline,8-carboxy quinoline, quinoaline, thiazole, and tryptophan; and aliphaticamines and substituted aliphatic amines (including carboxy-substitutedaliphatic amines) such as arginine, aspartic acid, betaine,glycyl-2-amino-n-butyric acid, cystine, l-glutamic acid, glycine, glycylglycine, glycylglycyl glycine, leucyl glycine, methyl glycine, n-propylglycine, tetraglycyl glycine, hexamethylene diamine, histidine,carnosine, 2-amino isobutyric acid, isoleucine, leucine, glycyl leucine,norleucine, ornithine, serine, threonine, methionine, glycylalanine,methoxy alanine, and threonine.

[0030] Relatively strong bases can form too strong a complex withphotogenerated acid and, consequently, use of such bases can preventrelease of an activating amount of acid at typical post exposure baketemperatures. Therefore less suitable polar compounds for purposes ofthe present invention are relatively strong bases that upon complexingwith a photogenerated acid will not provide an activating amount of acidat typical post exposure bake temperatures. For example, bases having apK_(a) of about 9.0 or greater are less suitable for purposes of thesubject invention, and thus are excluded from the preferred embodimentsof the invention. Polar compounds having a pK_(a) of about 10.0 orgreater, or 11.0 or greater will be even less suitable; such strongbases will have limited utility in the processes of the invention, andthus are also excluded from the preferred embodiments of the invention.Such less suitable and strongly basic compounds include, for example,trialkylamines such as triethylamine; monoalkylamines such asethylamine,propylamine, butylamine, heptylamine, hexylamine, octylamine, andnonylamine; and other strong bases such as trimethylimidine,2-aminoethyl benzene, dimethyl glycine, and triamino propane.

[0031] The polar compounds of the invention may be used in bothpositive-acting and negative-acting radiation sensitive compositions,including positive-acting and if negative-acting photoresists. Positivetone compositions are generally based on a two component systemcomprising a resin binder and an acid generator compound. A preferredresin binder is a phenol-based polymer. Negative tone compositions aretypically three component systems comprising a resin binder, an acidgenerator compound and a crosslinking agent. As discussed, for anegative resist, the photogenerated acid catalyzes a reaction betweenthe crosslinker and a reactive hydrogen containing material such as aphenol-based resin.

[0032] Phenol-based polymers useful for these acid-generatingcompositions are known in the art and typically comprise novolak andpoly(vinylphenol) resins and copolymers of the same with styrene andalpha-methylstyrene. Novolak resins are thermoplastic condensationproducts of a phenol, a naphthol or a substituted phenol, such as,cresol, xylenol, ethylphenol, butylphenol, isopropyl methoxyphenol,chlorophenol, bromophenol, resorinol, naphthol, chloronaphthol,bromonaphthol or hydroquinone with formaldehyde, acetaldehyde,benzaldehyde, furfural acrolein, or the like. Suitable novolak resinsare disclosed in U.S. Pat. Nos. 3,148,983; 4,404,357; 4,115,128;4,377,631; 4,423,138; and 4,424,315, the disclosures of which areincorporated herein by reference.

[0033] Poly(vinylphenol) resins are thermoplastic polymers that may beformed by block polymerization, emulsion polymerization or solutionpolymerization of the corresponding monomers in the presence of acationic catalyst. Vinylphenols useful for the production ofpoly(vinylphenol) resins may be prepared, for example, by hydrolysis ofcommercially available coumarin or substituted coumarins, followed bydecarboxylation of the resulting hydroxy cinnamic acids. Usefulvinylphenols may also be prepared by dehydration of the correspondinghydroxy alkyl phenols or by decarboxylation of hydroxy cinnamic acidsresulting from the reaction of substituted or non-substitutedhydroxybenzaldehydes with malonic acid. Preferred poly(vinylphenol)resins prepared from such vinylphenols have a molecular weight range offrom about 2,000 to about 100,000 daltons.

[0034] Another preferred phenol-based resin for the radiation sensitivecompositions of the invention are copolymers of phenols and nonaromaticcyclic alcohols analogous in structure to the novolak resins and thepoly(vinylphenol) resins. Such copolymers provide a radiation sensitivecomposition with relatively greater transparency to activatingradiation. These copolymers may be formed in several ways. For example,in the conventional preparation of a poly(vinylphenol) resin, a cyclicalcohol may be added to the reaction mixture during the polymerizationreaction which is thereafter carried out in normal manner. The cyclicalcohol is preferably aliphatic, but may contain one or two doublebonds. The cyclic alcohol is preferably one closest in structure tophenol. For example, if the resin is poly(vinylphenol), the comonomerwould be vinyl cyclohexanol.

[0035] The preferred method for formation of the copolymer compriseshydrogenation of a preformed novolak resin or a preformedpoly(vinylphenol) resin. Hydrogenation may be carried out using artrecognized hydrogenation procedures, for example, by passing a solutionof the phenolic resin over a reducing catalyst such as a platinum orpalladium coated carbon substrate or preferably over Raney nickel atelevated temperature and pressure. The specific conditions are dependentupon the polymer to be hydrogenated. More particularly, the polymer isdissolved in a suitable solvent such as ethyl alcohol or acetic acid,and then the solution is contacted with a finely divided Raney nickelcatalyst and allowed to react at a temperature of from about 100 to 300°C. at a pressure of from about 50 to 300 atmospheres or more. The finelydivided nickel catalyst may be a nickel-on-silica, nickel-on-alumina, ornickel-on-carbon catalyst depending upon the resin to be hydrogenated.Hydrogenation is believed to reduce the double bonds in some of thephenolic units resulting in a random copolymer of phenolic and cyclicalcohol units randomly interspersed in the polymer in percentagesdependent upon the reaction conditions used.

[0036] The mole percentage of cyclic alcohol units of the polymer shouldnot exceed a level where development of the radiation sensitivecomposition is prevented following exposure of the composition toactivating radiation. Thus, preferably the polymer has a majorproportion of phenolic units and a minor proportion of cyclic alcoholunits, more preferably the cyclic alcohol units vary from about 1 to 30mole percent of the polymer binder, and still more preferably from about5 to 15 mole percent of the polymer.

[0037] Other resins suitable for the practice of the invention includepolymers made from polystyrene maleimides with pendant acid labilefunctionalities. Examples of useful polymers include those disclosed inU.S. Pat. Nos. 4,931,379, and 4,939,070, both incorporated herein byreference. Vinylic polymers containing recurrent pendant group are alsouseful and are disclosed in U.S. Pat. No. 4,491,628, incorporated hereinby reference.

[0038] Another suitable resin is polyglutarimides, prepared according toU.S. Pat. No. 4,246,374, incorporated herein by reference, having aweight average molecular weight ranging from about 1000 to about 100,000and which are soluble in aqueous base and contain at least 40 weightpercent of the nitrogen atoms of the NH or ammonia form.

[0039] Another suitable resin binder for use in accordance with theinvention are phenol-based polymers that are partially silylated. Apreferred silylated polymer is disclosed in U.S. Pat. No. 4,791,171,incorporated herein by reference. This patent discloses partiallysilylated poly(vinylphenol) polymers prepared by derivatizing thephenolic hydroxide moieties of a poly(vinylphenol) with suitableorganosilicon compounds. Such derivatization can be accomplished, forexample, by condensation of a poly(vinylphenol) with an organosiliconcompound that has a suitable leaving group, for exampletrimethylsilylmethylchloride, bromide, mesylate or tosylate;trimethylsilylchloride, bromide, cyanide or mesylate;phenyldimethylsilylchloride; or t-butyldimethylsilylchloride.

[0040] For the positive tone radiation sensitive compositions, preferredacid generators are naphthoquinone diazide sulfonic acid esters such asthose disclosed by Kosar, Light Sensitive Systems, John Wiley & Sons,1965, pp. 343 to 352, incorporated herein by reference. This group ofacid generators form an acid in response to radiation of differentwavelengths ranging from visible to X-ray. Thus, the generator compoundchosen will depend, in part, upon the wavelengths used for exposure. Byselecting the appropriate acid generator, the radiation sensitivecompositions can be imaged by deep UV, E-beam, laser or any otheractivating radiation conventionally used for imaging photoresists.Specifically preferred acid generators include the2,1,4-diazonaphthoquinone sulfonic acid esters and the2,1,5-diazonaphthoquinone sulfonic acid esters.

[0041] Onium salts are also suitable acid generators for use in thecompositions of the invention. Onium salts, with weakly nucleophilicanions are particularly suitable. Examples of such anions are thehalogen complex anions of divalent to heptavalent metals or non-metals,for example, Sb, Sn, Fe, Bi, Al, Ga, In, Ti, Zr, Sc, D, Cr, Hf, and Cuas well as B, P, and As. Examples of suitable onium salts arediaryldiazonium salts and onium salts of group Va and B, Ia and B and Iof the Periodic Table, for example, halonium salts, quaternary ammonium,phosphonium and arsonium salts, aromatic sulfonium salts and sulfoxoniumsalts or seleonium salts. Examples of suitable preferred onium salts canbe found in U.S. Pat. Nos. 4,442,197; 4,603,101; and 4,624,912, allincorporated herein by reference.

[0042] A particularly suitable group of acid generating compounds usefulin the compositions of the invention are the iodonium salts. A preferredgroup of such salts are those resulting from the condensation ofaryliodosotosylates and aryl ketones as disclosed, for example, in U.S.Pat. No. 4,683,317, incorporated herein by reference.

[0043] Other useful acid generators include the family of nitrobenzylesters, and the s-triazine derivatives. Suitable s-triazine acidgenerators are disclosed, for example, in U.S. Pat. No. 4,189,323,incorporated herein by reference.

[0044] Dissolution inhibitors compounds also may be added to theradiation sensitive compositions of the invention to further controldissolution of an exposed coating layer of the composition. Suitabledissolution inhibiting compounds include, for example,t-butyloxycarbonato-bis-phenol-A and t-butylacetoxy-bis-phenol-A. Thedissolution inhibiting compounds may be suitably used in a concentrationof about 5 to 10 weight percent of total solids of a radiation sensitivecomposition.

[0045] As noted above, negative acid-hardening resist systems generallycomprise three components where photogenerated acid catalyzes a reactionbetween a crosslinker and a reactive hydrogen containing material suchas a phenol-based resin. All of the above described resins are suitableas the reactive hydrogen containing material for the negative-actingcompositions of the invention. Preferred are the above described novolakand poly(vinylphenol) resins. A particularly preferred resin fornegative tone compositions is the above described phenol-based polymerthat contains both phenolic and cyclic alcohol units.

[0046] In the negative resist systems, amine-based crosslinkers arepreferred. Suitable amine-containing crosslinkers includeurea-formaldehyde, melamine-formaldehyde, benzoguanamine-formaldehyde,glycoluril-formaldehyde resins and combinations thereof. Other suitableamine-based crosslinkers include the melamines manufactured by AmericanCyanamid Company such as Cymel^(R) 300, 301, 303, 350, 370, 380, 1116and 1130; benzoguanamine resins such as Cymel^(R) 1123 and 1125;glycoluril resins Cymel^(R) 1170, 1171, 1172; and urea-based resinsBeetle^(R) 60, 65 and 80. A large number of similar amine-basedcompounds are presently commercially available from various suppliers.As known to those in the art, polymeric amine-based resins may beprepared by the reaction of acrylamide or methacrylamide copolymers withformaldehyde in an alcohol-containing solution, or alternatively by thecopolymerization of N-alkoxymethyl acrylamide or methacrylamide withother suitable monomers.

[0047] Of the above crosslinkers, the melamines are preferred, andparticularly preferred are hexaalkoxymethylmelamines such as the aboveidentified Cymel resins.

[0048] The amine-based crosslinker and phenol-based polymer are used incombination with an acid generator. Non-ionic, organic acid generatorsare particularly suitable for the negative-acting compositions of theinvention. Particularly preferred non-ionic organic acid generators arehalogenated non-ionic compounds such as, for example,1,1-bis[p-chlorophenyl]-2,2,2-trichloroethane (DDT);1,1-bis[p-methoxyphenyl]-2,2,2-trichloroethane (methoxychlor^(R));1,2,5,6,9,10-hexabromocyclododecane; 1,10-dibromodecane;1,1-bis[p-chlorophenyl]2,2-dichloroethane;4,4′-dichloro-2-(trichloromethyl)benzhydrol or 1,1-bis(chlorophenyl)2-2,2-trichloroethanol (Kelthane^(R)); hexachlorodimethylsulfone;2-chloro-6-(trichloromethyl)pyridine;O,O-diethyl-O-(3,5,6-trichloro-2-pyridyl)phosphorothioate (Dursban^(R));1,2,3,4,5,6-hexachlorocyclohexane;N(1,1-bis[p-chlorophenyl]-2,2,2-trichloroethylacetamide;tris[2,3-dibromopropyl]isocyanurate;2,2-bis[p-chlorophenyl]-1,1-dichloroethylene; and their isomers,analogs, homologs and residual compounds. Suitable photoacid generatorsare also disclosed in European Patent Application Nos. 0164248 and0232972, both incorporated herein by reference.

[0049] Residual compounds are intended to include closely relatedimpurities or other modifications of the above halogenated organiccompounds which result during their synthesis and which may be presentin minor amounts in commercial products containing a major amount of theabove compounds.

[0050] Acid generators that are particularly preferred for deep UVexposure (i.e., about 100 to 300 nm) include1,1-bis(p-chlorophenyl)-2,2,2-trichloroethane (DDT);1,1-bis(p-methoxyphenol)-2,2,2-trichloroethane;1,1-bis(chlorophenyl)-2,2,2-trichloroethanol;tris(1,2,3-methanesulfonyl)benzene; and tris(trichloromethyl) triazine.

[0051] For negative-tone resist systems, the amine-based crosslinkingagent may be used as the basic substance to enhance resolution of arelief image of the resist. Again, the basicity of the crosslinkingagent should be such that the base holds the generated photoacid at roomtemperature and then releases an activating amount of acid at theelevated temperatures of the post-exposure bake. Suitable crosslinkersthat will release at least some photogenerated acids at post exposurebake temperatures include the melamine-formaldehyde resins such ashighly methylated melamine-formaldehyde, partially methylatedmelamine-formaldehyde, and mixed ether and butylated melamine resins. Ofthese melamine-formaldehyde resins, Cymel 303 (as commercially availablefrom American Cyanamid Co.) is specifically preferred.

[0052] It has been found that photoacid-generating compositions canprovide well resolved relief images, even with extended time delaysbetween the exposure and post exposure bake processing steps, where thecompositions comprise crosslinking agents of hexamethoxymethylmelamine(sometimes referred to herein as “HMMM”), hydrolyzed derivatives of HMMMwhich contain free amine moieties, and condensation products of HMMMincluding dimers and trimers of HMMM. Such HMMM derivatives have beendescribed in J. H. Dijk, et al., Proc. XVtL FATIPEC Conqr., II, 326(1980), incorporated herein by reference. It has also been found thatwhen a pure sample of HMMM is used as the sole crosslinking agent (i.e.,in the absence of any hydrolyzed HMMM derivatives or HMMM condensationproducts) in a photoacid-generating composition, a relief image isprovided having inferior resolution relative to the resolution of arelief image formed from a generally comparable composition thatcomprises HMMM, hydrolyzed HMMM derivatives, and HMMM condensationproducts. This is believed to indicate that an unhydrolyzed monomer ofHMMM does not complex with photogenerated acid and thus does not limitdiffusion of photogenerated acid. In turn, it is believed this resultindicates that hydrolyzed HMMM derivatives and/or HMMM condensationproducts such as dimers and trimers of HMMM effectively complex withphotogenerated acid, and that an activating amount of acid is liberatedfrom said complex at post exposure bake temperatures. Hence a preferrednegative acting radiation sensitive composition in accordance with theinvention comprises HMMM, HMMM condensation products, and hydrolyzedderivatives of HMMM that contain one or more amine groups that caneffectively complex with photogenerated acid. It is noted that Cymel 303as obtained from the American Cyanamid Co. comprises HMMM as well asboth hydrolyzed derivatives of HMMM which contain one or more aminegroups and HMMM condensation products such as dimers and trimers ofHMMM.

[0053] To enhance resolution of a patterned resist image, a polarcompound of the above described type may also be used in combinationwith a crosslinking agent such as a melamine-formaldehyde resin. Theterm “complexing polar compound”, or in the specific case of an amine a“complexing amine”, is defined to mean herein a polar compound of theinvention as described above, used in combination with and in additionto any conventional components of a radiation sensitive composition. Forexample, in a positive-acting composition, a complexing polar compoundwill be a component of the composition other than the resin binder, acidgenerator and any other conventional additives such as conventional dyesand conventional sensitizers for expanding the composition's spectralresponse. In a negative-acting composition a complexing polar compoundwill be a component of the composition other than a melamine resin orother primary crosslinker, resin binder, acid generator, conventionalsensitizers, conventional dyes or other conventional components of thecomposition. Amines are preferred complexing polar compounds for use incombination with the primary crosslinking agent in a negativephotoresist, and particularly preferred is a negative photoresist thatcomprises a complexing polar compound of an imidazole in combinationwith a primary crosslinker of a melamine resin.

[0054] Negative photoresists that employ a melamine crosslinker andphenol-based resin binder often provide somewhat limited resolution withmany acid generators that produce hydrogen halides (e.g., HBr) uponphotoactivation. Exemplary hydrogen halide generators includetris[2,3-dibromopropyl]isocyanurate. Such resolution problems arebelieved to result at least in part from diffusion of the photogeneratedhydrogen halide into unexposed regions during the interval betweenexposure and the post exposure bake crosslinking reaction. Byincorporating a suitable polar compound into such a photoresistcomposition that contains a hydrogen halide-generator compound,resolution improves. Preferred polar compounds for addition to a resistthat contains a hydrogen halide-generator compound include the abovedescribed amines.

[0055] The compositions of the invention are generally preparedfollowing prior art procedures for the preparation of photoresists andother photocurable compositions. For a liquid coating composition, thesolids portion of the composition is conventionally dissolved in asolvent. The solvent used does not constitute a part of the invention.However, for purposes of exemplification, useful solvents include glycolethers, such as ethylene glycol monomethyl ether, ethylene glycolmonoethyl ether, ethylene glycol dimethyl ether, methoxy benzene and thelike; Cellosolve^(R) esters such as methyl Cellosolve acetate, ethylCellosolve acetate and propylene glycol monomethyl ether acetate;aromatic hydrocarbons such as toluene, xylene and the like; ketones suchas acetone, methyl ethyl ketone, cyclopentanone, cyclohexanone; esterssuch as ethyl acetate, butyl acetate, hexyl acetate, isobutylisobutyrate and butyl lactone; amides such as dimethylacetamide,N-methyl pyrrolidione and dimethyl formamide; chlorinated hydrocarbonssuch as methylene chloride, ethylene dichloride, 1,1,1-trichloroethane,chlorobenzene and ortho-dichlorobenzene; nitrobenzene; dimethylsulfoxide; alcohols such as diacetone alcohol; and mixtures of theforegoing.

[0056] Effective results (e.g., enhanced resolution of a relief image)can be achieved if one or more polar compounds of the above describedtype is added to a conventional photoresist composition in an amount offrom about 0.05 to 5.0 weight percent, although it should be clear thateffective amounts may vary with the particular composition and polarcompound(s) that are employed.

[0057] The total solids content of the liquid coating compositions ofthe invention should not exceed about 60 percent by weight of theformulation and preferably, the solids content varies between about 10and 50 percent by weight of the total composition.

[0058] The compositions of the invention are used in a conventionalmanner and for conventional purposes. The liquid coating compositions ofthe invention are applied to a substrate such as by spinning, dipping,roller coating or other conventional coating technique. When spincoating, the solids content of the coating solution can be adjusted toprovide a desired film thickness based upon the specific spinningequipment utilized, the viscosity of the solution, the speed of thespinner and the amount of time allowed for spinning.

[0059] The compositions of the invention are applied to substratesconventionally used in processes involving coating with photoresists.For example, the compositions of the invention may be applied oversilicon or silicon dioxide wafers for the production of microprocessorsand other integrated circuit components. Aluminum—aluminum oxide andsilicon nitride wafers can also be coated with the compositions of theinvention. Another suitable use of the compositions of the invention isas a planarizing layer or for formation of multiple layers in accordancewith art recognized procedures.

[0060] For typical photoresist applications, following coating of acomposition of the invention onto a surface, it is subjected to apre-exposure soft bake, i.e. heated to about 90° C. to remove thesolvent until preferably the resist coating is tack free. Thereafter, itis imaged through a mask in conventional manner. The exposure issufficient to effectively activate the photoactive component of theresist system to produce a patterned image in the resist coating layerand, more specifically, the exposure energy typically ranges from about10 to 300 mJ/cm², dependent upon the exposure tool. The wavelength ofactivating radiation will, of course, vary with the photoactivecomponents of a given radiation sensitive composition and will be knownto those skilled in the art. The spectral response of a radiationsensitive composition can be expanded by the use of suitable radiationsensitizer compounds.

[0061] Following exposure, the composition is preferably baked attemperatures ranging from about 50° C. to about 140° C. to release anactivating amount of acid from the complex of the polar compound and thephotogenerated acid, and effect the acid-catalyzed reaction. Preferablythe activating amount of acid released from the polarcompound-photogenerated acid complex during post exposure bake issufficient to catalyze a reaction that results in a solubilitydifferential of preferably at least about 10:1, more preferably at leastabout 100:1, between exposed and unexposed regions of a coating layer ofthe radiation sensitive composition. Thereafter, the film is developed,preferably with an aqueous based developer such as an inorganic alkaliexemplified by sodium hydroxide, potassium hydroxide, sodium carbonate,sodium bicarbonate, sodium silicate, sodium metasilicate, aqueousammonia or the like. Alternatively, organic developers can be used suchas choline based solutions; quaternary ammonium hydroxide solutions suchas a tetra-alkyl ammonium hydroxide solution; various amine solutionssuch as ethyl amine, n-propyl amine, diethyl amine, di-n-propyl amine,triethyl amine or methyldiethyl amine; alcohol amines such as diethanolamine or triethanol amine; cyclic amines such as pyrrole, piperidine,etc. In general, development is in accordance with art recognizedprocedures.

[0062] Following development, a bake at temperatures of from about 100°C. to about 250° C. for several minutes may be employed if desired.

[0063] The developed substrate may then be selectively processed onthose substrates areas bared of the coating composition, for examplechemically etching or plating substrate areas bared of the compositionin accordance with procedures well known in the art. For the manufactureof microelectronic substrates, for example the manufacture of silicondioxide wafers, suitable etchants include a plasma gas etch and ahydrofluoric acid etching solution. The compositions of the inventionare highly resistant to such etchants thereby enabling manufacture ofhighly resolved features, including lines with submicron widths. Aftersuch processing, the composition mask may be removed from the processedsubstrate using known stripping procedures.

[0064] The following examples are presented to better illustrate theinvention, but are not to be construed as limiting the invention to thespecific embodiments disclosed.

[0065] Throughout the examples, the partially hydrogenatedpoly(p-vinylphenol) resins were obtained from Maruzen Oil, Co. of Tokyo,Japan. The degree of hydrogenation of these poly(p-vinyl phenols) isexpressed as % of aromatic double bonds converted to single bonds, orequivalently as % of hydroxyphenyl groups converted to hydroxycyclohexylgroups. All temperatures throughout this disclosure are in degreesCelsius.

EXAMPLE 1

[0066] A photoresist composition was prepared consisting of 10 g ofpoly(p-vinyl)phenol (hereafter “PVP”) at a 10% level of hydrogenation, 2g of t-butyloxycarbonato-bis-phenol-A and 1.5 g oftris(1,2,3-methane-sulfonyl) benzene dissolved in 27.5 g of diethyleneglycol dimethyl ether. This resist formulation was coated to 1.0 micronthickness on three separate silicon wafers (hereafter “the first wafer”,“second wafer” and “third wafer”) using a conventional spin coater. Thewafers were each soft baked at 90° C. for 1 minute, and then exposed for10 seconds on an HTG deep UV exposure unit with a variable opticaldensity mask placed between the source and the wafer. The first waferwas subjected to a time delay between exposure and post exposure bake of5 minutes; the second wafer was subjected to a time delay of 120minutes; and the third wafer was subjected to a time delay of 24 hoursbetween exposure and post exposure bake. All three wafers were postexposure baked at 120° C. for 1 minute. The three wafers were then batchdeveloped in MF-321 (tetramethylammonium hydroxide sold by ShipleyCompany of Newton, Mass.) for 60 seconds. For the first and secondwafers with delay times of 5 and 60 minutes, respectively, the contrastcurves overlapped. For the third wafer stored for 24 hours, it wasobserved that the resist slowed down as a function of the delay betweenexposure and post exposure bake. Further, in the case of the thirdwafer, the photoresist became, for practical purposes, insoluble in thedeveloper. While not wishing to be bound by theory, it is believed thisresult indicates slow diffusion of acid in the unexposed areas leadingto lower concentration of acid in the exposed areas during the bake stepand thereby decreasing the number of blocked sites deprotected in theexposed areas.

EXAMPLE 2

[0067] 0.1 g of triisopropanol amine was added to 50 g of thephotoresist composition prepared in Example 1. This photoresist wascoated on three separate silicon wafers and processed by the sameprocedures as described in Example 1. The third wafer subjected to atime delay of 24 hours between exposure and post exposure bake showed nochange in the contrast curve relative to the first and second waferssubjected to the shorter time delays. It is believed this resultindicates that the base complexes with the photogenerated acid,confining the acid to exposed areas to provide a sufficient acidconcentration to deprotect the t-Boc sites during the post exposurebake.

EXAMPLE 3

[0068] A photoresist composition was prepared by mixing 10 g of PVP at10% hydrogenation, 0.75 g of purified hexamethoxymethylmelamine, and 0.5g tris(trichloromethyl)triazine dissolved in 28.25 g diethylene glycoldimethyl ether. The resist was coated to 1.0 micron thickness on threeseparate silicon wafers using a conventional spin coater. The waferswere then baked at 90° C. for 1 minute, and then exposed on a GCA ALSLaserstep 5:1 excimer laser stepper. The first wafer was subjected to atime delay between exposure and post exposure bake of 5 minutes; thesecond wafer was subjected to a time delay of 120 minutes; and the thirdwafer was subjected to a time delay of 24 hours. All three wafers werepost exposure baked at 130° C. for 1 minute. The wafers were batchdeveloped in 0.135 N MF-312 (tetramethyl ammonium hydroxide) for 150seconds. As a measure of diffusion, the changes in linewidth of a 0.5micron feature were observed during the time delay between exposure andpost exposure bake. The line width change increased with increasing timedelay between exposure and post exposure bake. For the wafer subjectedto the 24 hour time delay, the 0.5 micron linewidth was reduced to 0.2micron. While again not wishing to be bound by theory, it is believedthis loss of linewidth resulted from diffusion of acid into theunexposed regions of the resist coating layer, leading to less acid inthe exposed areas and hence linewidth shrinkage as if the resist layerhad been underexposed.

EXAMPLE 4

[0069] A photoresist composition was prepared by adding 0.1 g of2-methylimidazole to 50 g of the photoresist composition prepared inExample 3. This imidazole photoresist composition was coated on threeseparate silicon wafers and processed by procedures the same as thosedescribed in Example 3 with time delays between exposure and postexposure bake of 5 minutes, 120 minutes and 24 hours for the first,second and third wafers, respectively. Upon development, no linewidthloss for any of the three wafers was observed. This result is believedto demonstrate that the imidazole base complexes with the photogeneratedacid at room temperature, confining the acid to exposed regions of theresist layer.

[0070] The foregoing description of the invention is merely illustrativethereof, and it is understood that variations and modifications can beeffected without departing from the scope or spirit of the invention asset forth in the following claims.

What is claimed is:
 1. A radiation sensitive composition, comprising aresin binder, an acid generator compound, and a complexing polarcompound.
 2. The composition of claim 1 where the polar compoundcomprises one or more moieties selected from the group consisting ofethers, esters, amides and amines.
 3. The composition of claim 1 wherethe polar compound is an amine.
 4. The composition of claim 1 comprisinga phenol-based polymer, an amine-based crosslinking agent, and acomplexing amine.
 5. The composition of claim 1 where the polar compoundhas a pK_(a) of about 8.0 or less.
 6. The composition of claim 1 wherethe polar compound has a pK_(a) of about 4.0 or less.
 7. The compositionof claim 1 where the polar compound has a pK_(a) of about 3.2 or less.8. The composition of claim 1 where the resin binder is a phenol-basedpolymer.
 9. The composition of claim 1 where the resin binder isselected from the group consisting of (1) novolak resins, (2)poly(vinylphenol) resins, (3) phenol-based polymers comprising phenolicunits and cyclic alcohol units, (4) polyglutarimides, (5) silylatedphenol-based polymers, and (6) polymers made from polystyrene maleimideswith pendant acid labile functionalities.
 10. A method for treating aphotoacid-generating composition, comprising adding a complexing polarcompound to the composition.
 11. The method of claim 10 where the polarcompound is an amine.
 12. The method of claim 10 where the polarcompound has a pK_(a) of about 8.0 or less.
 13. The method of claim 10where the polar compound has a pK_(a) of about 4.0 or less.
 14. Themethod of claim 10 where the polar compound has a pK_(a) of about 3.2 orless.
 15. The method of claim 10 further comprising applying a layer ofthe composition to a substrate; exposing the composition layer toactivating radiation; and heating the composition layer to a temperaturesufficient to provide an activating amount of acid.
 16. The method ofclaim 15 where said exposing generates a latent image in the compositionlayer comprising acid moieties complexed with the polar compound. 17.The method of claim 10 where the composition comprises hexamethoxymethylmelamine, condensation products of hexamethoxymethyl melamine, andhydrolyzed derivatives of hexamethoxymethyl melamine, said hydrolyzedderivatives containing one or more amine groups.
 18. A method forenhancing resolution of a photoacid-generating composition, comprisingadding a polar compound to the composition, the polar compound having apK_(a) of about 8.0 or less.
 19. The method of claim 18 where the polarcompound is a complexing polar compound.
 20. The method of claim 18where the polar compound is an amine.
 21. The method of claim 18 wherethe polar compound has a pK_(a) of about 4.0 or less.
 22. The method ofclaim 18 where the polar compound has a pK_(a) of about 3.2 or less. 23.The method of claim 18 further comprising applying a layer of thecomposition to a substrate; exposing the composition layer to activatingradiation; and heating the composition layer to a temperature sufficientto provide an activating amount of acid.
 24. The method of claim 23where said exposing generates a latent image in the composition layercomprising acid moieties complexed with the polar compound.
 25. Themethod of claim 18 where the composition comprises hexamethoxymethylmelamine, condensation products of hexamethoxymethyl melamine, andhydrolyzed derivatives of hexamethoxymethyl melamine, said hydrolyzedderivatives containing one or more amine groups.
 26. A method forcontrolling acid diffusion of a photoacid-generating composition,comprising: (a) adding a polar compound to the composition and applyinga layer of the composition to a substrate; (b) exposing the compositionlayer to activating radiation whereby a latent image is generatedcomprising acid moieties complexed with the polar compound; and (c)treating the exposed composition layer to provide an activating amountof acid.
 27. The method of claim 26 where the exposed composition layeris treated by heating to a temperature sufficient to provide anactivating amount of acid.
 28. The method of claim 27 where thecomposition is heated to a temperature of about 50° C. or greater. 29.The method of claim 27 where the composition is heated to a temperatureof about 100° C. or greater.
 30. The method of claim 27 where thecomposition is heated to a temperature of about 110° C. or greater. 31.The method of claim 26 further comprising, prior to the exposing step,baking the composition layer to remove solvent while an effective amountof the polar compound remains disposed in the resist layer.
 32. Themethod of claim 31 where the composition is baked at a temperature ofabout 90° C. or less.
 33. The method of claim 26 where the polarcompound comprises one or more moieties selected from the groupconsisting of ethers, esters, amides and amines.
 34. The method of claim26 where the polar compound is a complexing polar compound.
 35. Themethod of claim 26 where the polar compound has a pK_(a) of about 8.0 orless.
 36. The method of claim 26 where the polar compound has a pK_(a)of about 4.0 or less.
 37. The method of claim 26 where thephotoacid-generating composition comprises a radiation sensitivecomponent and a resin binder selected from the group consisting of (1)novolak resins, (2) poly(vinylphenol) resins, (3) phenol-based polymerscomprising phenolic units and cyclic alcohol units, (4)polyglutarimides, (5) silylated phenol-based polymers, and (6) polymersmade from polystyrene maleimides with pendant acid labilefunctionalities.
 38. The method of claim 26 where the composition is anegative-acting photoresist comprising a phenol-based resin, anamine-based crosslinking agent, and an acid generator compound.
 39. Themethod of claim 26 where the composition comprises hexamethoxymethylmelamine and hydrolyzed derivatives of hexamethoxymethyl melamine, saidhydrolyzed derivatives containing one or more amine groups.
 40. A methodfor forming a relief image comprising: (a) applying a layer of aradiation sensitive composition to a substrate, the compositioncomprising a resin binder, an acid generator compound, and a complexingpolar compound; and (b) exposing and developing the composition layer onthe substrate to yield a relief image.
 41. The method of claim 40further comprising metallizing or etching substrate areas bared of thecomposition upon development.
 42. The method of claim 40 where thesubstrate comprises one or more materials selected from the groupconsisting of silicon, silicon dioxide, silicon nitride, aluminum andaluminum oxide.
 43. An article of manufacture produced by the process ofclaim 40 .